On January 6, 2015, at a meeting of the American Astronomical Society, a team of scientists (analyzing data from NASA's Kepler Space Telescope) announced the discovery of eight new planets orbiting in or near the habitable zone of their host stars in Constellation Lyra.
The two most Earth-like planets discovered are Kepler 438 b and Kepler 442 b, and both orbit orange to red dwarf stars that are smaller and cooler than our Sun. Kepler 438 b circles its star every 35 days, while Kepler 442 b completes one orbit every 112 days. With a diameter just 12 percent bigger than Earth, Kepler 438 b has a 70-percent chance of being rocky, while Kepler 442 b is about a third larger than Earth (probably a super-Earth), but still has a 60-percent chance of being rocky (CfA
new release; and
Torres et al, 2015).

On August 25, 2014, a team of astronomers submitted a paper revealing the discovery of a super-Earth around Groombridge 34 A in a tight inner orbit. Planetary candidate "b" has around 5.35 ± 0.75 Earth-masses and an orbital period that is a little longer than 11.4 days, which appears to be relatively circular (e= 0.12 +0.08/-0.06). Planet b's orbit around Star A has a semi-major axis of only 0.0717 +/- 0.0034 AUs
(Howard et al, 2014).

On June 21, 2014, a team of astronomers submitted a preprint which revealed their detection of a super-Earth around CD-49 13515 (or Gl 832). Designated "c" after a previously discovered Jupiter-class planet b in a cold outer orbit, planet c has about 5.4 +/- 1.0 Earth-masses, an orbital period of 35.68 +/- 0.03 days at a semi-major axis of 0.163 +/- 0.006 AU, an orbital eccentricity of e= 0.18 +/- 0.13, and an orbital distance near the inner edge of its host star's habitable zone. If it has an Earth-like terrestrial atmosphere, planet c may have Earth-like temperatures with possibly with large seasonal shifts, given a similar terrestrial atmosphere, but a denser atmosphere as would be expected for massive super-Earths could easily make the planet too hot for life and more akin to a super-Venus instead
(Sci-News.com, June 29, 2014;
Astronomy
Picture of the Day; and
Wittenmyer et al, 2014).

Planet "c" appears to be
a super-Earth
with sufficient mass to attract a dense
atmosphere and so may resemble a hot
super-Venus
(more).

On June 3, 2014, a team of astronomers reported the discovery of two super-Earths orbiting ancient Kapteyn's Star. Kapteyn b might support liquid water on is surface, although it has at least 4.8 Earth-masses and completes its orbit within only 48.6 days at an average orbital distance of 0.17, with an orbital eccentricity of 0.21. Kapteyn c is even more massive at a minimum of 7.0 Earth-masses and its year lasts 121.5 days at an average orbital distance of 0.31, with an orbital eccentricity of 0.23, and should be too cold to support liquid water.
(CIS
news release; and
Anglada-Escudé
et al, 2014).

Two super-Earths have been detected around
Kapteyn's Star (an orphan star torn from an
ancient dwarf satellite galaxy of the Milky
Way), one within its habitable zone
(more).

On March 4, 2014, a team of astronomers announced that analysis of new and older radial-velocity data from nearby red dwarf stars indicates that most such stars may have at least one planet below 10 Earth-masses each. In addition to 10 unconfirmed, weaker "signals," the team was able to detect eight super-Earths around red dwarfs between 15 and 80 light-years away from our Sun, Sol, of which three orbit within the habitable zones of their host stars. They calculate that such habitable-zone super-Earths may orbit around at least a quarter of the red dwarfs in the Solar neighborhood (UH
news release; and
Tuomi et al, 2014).

Three, possibly four, super-Earths
have been detected in the habitable
zone around Star C
(more), view of
daytime sky from planet "d" as
imagined by Kormmesser.

On June 25, 2013, astronomers announced the Gliese 667 C has at least six planets (possibly seven) and confirmed that at least three (possibly four) super-Earths (possibly four) orbit within the habitable zone around the star
(ESO
news release; and
Anglada-Escude
et al, 2013).

On February 2, 2011, the
Kepler Mission
revealed the detection of 54 potential
planetary
candidates which orbit their
host
star within or near its apparent habitable
zone -- where liquid water can exist on the surface of an
Earth-type planet. Although five of these planets are near Earth
in size, 16 are candidate super-Earths. While the other 33
are larger, some astronomers wonder if any of them have
moons that could be massive enough to support Earth-type
life (NASA/Kepler
press
release).

As of February 2, 2011, the
Kepler Mission
has found 16 super-Earths candidates
with orbits within, or near, their
host star's habitable zone
(more).

The 16
planetary
candidates have estimated diameters
within range of being super-Earths (1.26 to 2.0 times
Earth's diameter), given error margins ranging from 25 to 35 percent
due to the uncertainty in the size of their
host
star and of
the "depth" of the observed transits (decrease in stellar
luminosity) across the surface of the star. For each
planetary candidate, the equilibrium surface temperatures
are derived from "grey-body spheres without atmospheres ...
[and] calculations assume a Bond albedo of 0.3, emissivity
of 0.9, and a uniform surface temperature ... [with
uncertainties of] approximately 22% ... because of
uncertainties in the stellar size, mass, and temperature
as well as the planetary albedo." Actual planetary surface
temperature would likely be higher due to warming by any
atmosphere gases that might be present
(Borucki
et al, 2011, pp. 21-23, Table 6).

The table below lists Kepler's super-Earth candidates by
designation number as a "Kepler Object of Interest" (KOI).
This means that the object remains to be confirmed (as
opposed to confirmed planets listed as Kepler-number).
Also included in the table below is
Gl 581 g,
which is another super-Earth candidate in its host star's
habitable zone whose existence has not been confirmed.

On April 18, 2013, astronomers working on NASA's
Kepler
Mission announced their discovery of two planetary systems that appear to host three super-Earth-size planets (Kepler 62e, 62f, and 69c) in habitable-zone orbits, where the surface temperature of the planet may be suitable for liquid water. Although the
Kepler-62
system has five detected planets, the Kepler-69 system has only two thus far.
Kepler 62 is a K-2 dwarf star that is smaller, cooler, only a fifth as bright as our Sun,
Sol, while
Kepler 69 is a Sun-like G-type dwarf with perhaps 93 percent of its mass and 80 percent of its brightness. Kepler-62f is only 40 percent larger in diameter than Earth, making it the extra-Solar planet closest to Earth's size detected in the habitable zone of another star and is likely to have a rocky composition. Similarly, Kepler-62e orbits on the inner edge of its star's habitable zone and is roughly 60 percent larger than Earth. Modelling suggest that both 62e and 62f may be
"water
worlds" with global oceans. Kepler-69c may be around 70 percent larger than Earth, and its orbit of 242 days around its Sun-like star resembles that of Venus in the Solar System
(NASA
news
release; and Kepler
news
release).

On February 6, 2013, astronomers analyzing data from NASA's the Kepler Space Telescope announced that some six percent of red dwarf stars may have habitable, Earth-sized planets. Recalibrated for the size of their host star now calculated to be red dwarfs, one Earth-sized and two super-Earth planets were identified as orbiting within their stars' habitable zones. The three habitable-zone planetary candidates identified in this study are: Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5,700 and 5,900 degrees Fahrenheit (CfA
press release; and
Dressing and Charbonneau, 2013).

Analysis of Kepler
Mission
data indicates that 6 percent
of all red dwarf stars may
have Earth-like planets
(more).

On January 7, 2013, NASA's
Kepler Mission
announced the detection of 461 new planetary candidates.
Four are classed as super-Earths that may orbit within their host star's habitable zone. One (KOI 172.02) only has about 1.5
Earth's diameter and orbits a G-type star somewhat cooler than our Sun, Sol, at a distance of about 0.75 AU with a period of 242 days (Kepler
news
release).

As of January 7, 2013, the Kepler Mission
has detected
816 super-Earth-sized,
planetary candidates
(more).

On December 17, 2012, an astronomer submitted a preprint with new analysis of available radial-velocity data supporting the existence of five planetary candidates around Gliese 667 C. Two planetary candidates were previous detected with orbital periods of 7.2 and 28.1 days ("b" and "c'), while three additional orbital periods of 30.8, 38.8, and 91.3 days ("d," "e," and "f") are also likely to be associated with planetary companions around Gliese 667 C. If confirmed as planets, the 28.1-, 30.8-, and 38.8-day periods would be associated with objects orbiting in the "central portion of the habitable zone, while the 91.3 day orbits lies partly within the habitable zone." The minimum masses for b, c, d, e, and f are 5.4, 4.8, 3.1, 2.4, and 5.4 Earth-masses, respectively. If confirmed, planetary candiate "e" with a 38.8-day period with 2.4 Earth-masses is the lowest mass extra-Solar planet detected in a star's habitable zone to day
(Philip C. Gregory, 2012).

On November 7, 2012, a team of astronomers revealed the possible detection of three additional super-Earth-class around this star. Planetary candidates "e," "f," and "g" have a minimum of 3.5 to 7.1 Earth-masses, and their orbits have: average distances of 0.119, 0.247, and 0.600 AU; periods of 34.6, 51.8, and 197.8 days; and eccentricities of 0.15, 0.02, and 0.29, respectively. Orbiting at an average distance within its host star's habitable zone, candidate g has at least 7.1 Earth-masses and so may have a thick atmosphere more like Neptune in the Solar System
(Joanna
Carver, New Scientist, November 8, 2012);
BBC News, November 8, 2012; and
Tuomi et al, 2012).

Planetary candidate "g" may
be a super-Earth with a
habitable-zone orbit
(more).

On August 29, 2012, the Planetary
Habitability Laboratory (PHL) revealed that a team of astronomers working with the
High Accuracy Radial velocity Planet Search (HARPS) project had discovered two planets "b" and "c" around the red dwarf star Gliese 163. Gliese 163 c is a super-Earth with a minimum of 6.9 Earth-masses and a diameter between 1.8 and 2.4 times that of Earth. Located just inside the inner edge of Gliese 163's habitable zone, planet c completes an orbit around its host star in less than 26 days. Receiving on average about 40 percent more light from its host star than Earth does from Sol, planet c has an average surface temperature of about 60°C, compared with Earth's 50°C (PHL
press
release).

As of August 29, 2012, the most
habitable super-Earth may be Gliese 581 "g",
among five
other super-Earths near or
within the habitable zone of
their host stars
(more).

On July 19, 2012, the Planetary
Habitability Laboratory (PHL) announced that new
data and analysis suggest that the most
habitable super-Earth known on that date may be
Gliese 581 g,
among four other super-Earths
near or within the habitable zone of their host stars.
Although the nearby star Gliese 581 is already known for having
at least four planets, with Gliese 581 d already suspected of having a habitable orbit, there is now evidence there are two potentially habitable exoplanets orbiting the same star. Both
planets are included among the five most habitable found thus far using PHL criteria, including
Gliese 667 Cc, Kepler-22 b, and HD 85512 b (PHL
press
release).

On March 28, 2012, astronomers working with the
European Southern Observatory's HARPS instrument announced that super-Earths with habitable-zone orbits may be found in about 41 percent (within a range of 28 to 95 percent) of dim red dwarf (spectral class M) stars within 30 light-years of our Sun. Previously discussed in a November 24, 2011 pre-print, the astronomers "surveyed a carefully chosen sample of 102 red dwarf stars in the southern skies over a six-year period" and found a "total of nine super-Earths (planets with masses between one and ten times that of Earth)," of which two orbiting within the habitable zones of Gliese 581 and Gliese 667 C.
By combining all the radial-velocity data of red dwarf stars (including those without undetected planets) and examining the fraction of confirmed planets that was found, the astronomers were able to estimate the probable distribution of different types of planets around red dwarfs: for example, only 12 percent of such stars within 30 light-years may have giant planets with masses between 100 and 1,000 times that of the
Earth (ESO
news
release;
Bonfils et al, 2011; and
Delfosse et al, 2011).

Kepler 22b is a super-Earth candidate with
around 2.4 times Earth's diameter that orbits
a G5 star within its habitable zone
(more).

On December 5, 2011, astronomers working on the
Kepler Mission announced
their first confirmation an extra-Solar, super-Earth-sized planet
orbiting within the "habitable zone" of a distant Sun-like star
(spectral class G5), which was discovered using Kepler. Located
around 620 light-years away around a star somewhat smaller,
cooler, and roughly 25 percent dimmer than
Sol which was designated
"Kepler-22,"
planet "b" is estimated to have about 2.38 (+/- 0.13) times Earth's
diameter and has an orbital period around
Kepler 22 of about 290
days (with an average orbital distance of around 0.85 +/- 0.02AUs).
Scientists have not yet been able to determine whether Kepler-22
b has a predominantly rocky, gaseous, or liquid composition (NASA
news
release; Kepler
briefing and
discoveries; and
science
news).

As of February 2, 2011, NASA's Kepler Mission
has identified
1,235 planetary candidates based
on more than four months of
observations, of which many are
in 170 multi-planet systems and
54 may orbit within the habitable
zone of their host stars
(more).

On Wednesday, February 2, 2011, NASA's
Kepler Mission
revealed that, thus far, it has detected 1,235 planetary
candidates orbiting 907 host stars, from a survey of
some 155,453 stars in
constellations
Cygnus and Lyra using the transit method which
requires a rare orbital alignment across the face of
the host star as seen from the Solar System. Most of
these potential planets appear to be much smaller
than gas giants
(like Jupiter and
Saturn). They include
19 larger than Jupiter and 165 Jupiter-class objects,
662 Neptune-class
planets, 288 "super-Earths" (1.26 to 2.0 times Earth's diameter,
and 68 Earth-sized planets (0.5 to 1.25 times Earth's diameter) (NASA/Kepler
press
release;
Borucki
et al, 2011; and
Lissauer et al, 2011a).

As of February 2, 2011,
Kepler's
planetary candidates have been
identified from only some four
and a half months of observation,
and so the orbital periods of
these 1,235 potential planets
are relatively short
(more).

Many of these planets have been found to be members of some
170 multi-planet systems
(Lissauer et al,
2011a). Kepler's growing haul of planetary candidates
was derived from only four and a half months of observations
conducted between May 2 and Sept. 17, 2009. By comparison,
confirmation of an Earth-sized planet orbiting its host star
at a distance of one AU like the
Earth would take a full 12
months of observations, plus another year or two of repeated
observation to confirm the orbital period. Lastly, the
largest known planetary system other than the
Solar System was confirmed
to have at least six planets, which have tightly packed
orbits around an eight-billion-year-old star located some
2,000 light-years away and include four super-Earths:
Kepler-11b, "-11d, "-11e, and "-11f (Kepler
news
release;
Borucki
et al, 2011;
Lissauer
et al, 2011b; and
Rachel
Courtland, New Scientist, February 3, 2011
-- whose planetary and orbital characteristics are
summarized below).

NASA's Kepler Mission
has confirmed
its detection of a planetary system
(Kepler-11) with at least six planets,
including four super-Earths
(more).

An Evolving Concept

Fellow astronomers were quite surprised in 1990 when
Alex Wolszczan and 'Dale Frail announced the discovery of the
first
three planets outside the Solar
System around
PSR
B1257+12 during a
pulsars
survey
(Wolszczan
and Frail, 1992. Given then theories of planetary
formation, they had expected to find planets in orbit
around "normal" main sequence stars like our Sun,
Sol, instead of orbiting
stellar remnants like neutron stars which had undergone
supernovae. That two of the first three planets were
larger than Earth but
smaller than the Solar System's
four outer gas giants
was also unexpected. Not until 2005 did astronomers
finally announce the finding of a similarly sized
planet around a main sequence star, with the discovery
of Gliese (Gl)
876 d.

Gl 876 d
may be rocky and have
an atmosphere with clouds and the
glow of molten areas on its surface,
as imagined by Schindler
(more).

Using a lower bound of two Earth-masses,
astronomers have been increasingly relying
on the label "super-Earth" for extra-Solar
planets that are probably too large to be very
"Earth-like," despite their search for planets with
characteristics closer to the
Solar System's
four rocky inner,
"terrrestrial" planets than gas giants.
In addition, they have also relied on the predictions of
core-accretion models of planetary development that require
an upper bound of around 10 Earth-masses to avoid forming large planets that form a significant hydrogen-helium atmosphere
like the gas giants (beginning with
Uranus in the Solar System).
As additional super-Earths are discovered, researchers
has been debating whether additional criteria
(e.g., planetary radius or density) should be added
for making additional distinctions
(Seager
et al, 2007).

61 Virginis b has an inner
"torch" orbit that should
heat its atmosphere so
much that it glows
(more).

NASA's Kepler Mission
originally proposed to define the size of an
Earth-type planet to be one with
between 0.5 and 2.0 times Earth's mass, or one having between 0.8
and 1.3 times Earth's radius or diameter. The mission is also
focusing on larger terrestrial planets that have two to 10
Earth-masses, or 1.4 to 2.2 times its radius. While larger
planets could have sufficient gravity to attract a
massive hydrogen-helium atmosphere, smaller planets -- like Mars or
Mercury that have less than half
the Earth's mass -- located in or near their star's habitable zone
may lose their initial life-supporting atmosphere because of low
gravity and/or the lack of plate tectonics needed to recycle
heat-retaining carbon dioxide gas back into the atmosphere
(Kasting
et al, 1993). In contrast, super-Earths with a similar
concentration but larger absolute amount of radioactive heat
sources (i.e., uranium and thorium) than Earth would produce
more internal heat, more vigorous mantle convection, and faster
plate tectonic action involving thinner plates, which may
promote planetary habitability with lower mountain ranges but
higher volcanic activity and an atmosphere with a greater
relative composition of volcanic and lighter gases
(Sasselov
and Valencia, Scientific
American, August 2010;
Valencia
and O'Connell, 2009; and
Valencia et al,
2007).

Assuming an iron-rich planet with an internal structure
like Earth, modelling results for the first discovered
super-Earth
(GJ 876 d)
indicate the existence of a threshold in planetary
diameter above which a super-Earth "most certainly"
has a high water content (an "ocean planet" or
"water world," where thick layers of water and
pressurized ice surround a rocky mantle and core); this
threshold was found to be around 24,000 kilometers (or nearly 15,000
miles) in the particular case of GJ 876 d
(Valencia
et al, 2007). Given the same mass, ocean planets
are around 40 to 50 percent larger than rocky planets
(Fortney
et al, 2007). Water worlds, however, may be most
likely type of super-Earth to be habitable for
photosynthesis-based Earth-type life
(von
Bloh et al, 2009).

Many charged particles from the Sun's Solar Wind are trapped by Earth's
magnetic
field
to form its
magnetosphere,
deflecting the Wind from a head-on collision with its atmosphere.

In 2010, model simulations of rocky super-Earths
between two and 10 Earth-masses indicated that high
pressures could keep their cores solid instead of
molten, which would prevent a protective magnetic
field from forming protecting developing surface
life from stellar radiation. Without a magnetic
field generated by a rotating molten metallic core,
the atmosphere of such a planet would also face
progressive erosion by the stellar wind of its
host star. Other scientists caution that the
interiors of super-Earth may still get hot enough
to melt their iron cores despite the pressure due
to other factors not yet considered by the model
simulation
(New
Scientist, November 6, 2010; and
Morard et
al, 2010).

On January 26, 2012, scientists working on NASA's
Kepler Mission team announced
the discovery of 11 new planetary systems hosting 26 confirmed
planets, as well as additional planetary candidates. These
discoveries nearly double the number of confirmed planets discovered
using the Kepler space telescope and triple the number of stars known
to have more than one planet that "transits" in front of its host
star. Fifteen of the newly confirmed planets are estimated to be
only between Earth and
Neptune in size, and the smallest
may have a diameter only 50 percent larger than Earth's
(Kepler
33b). The smallest planet orbits
Kepler-33,
a star older and more massive than our Sun,
Sol, which also had the most
detected planet candidates at five (ranging in size from 1.5 to 5
times that of Earth) in uninhabitable, hot inner orbits closer to their star than even
Mercury around our Sun (NASA Kepler
news
release; and JPL
news
release).

On January 11, 2012, astronomers working with the
European Southern Observatory
(ESO) announced that most stars in our Milky Way Galaxy have planets.
They used
gravitational
microlensing to analyze how common planets may be around stars.
After six years of observation involving millions of stars, they
concluded "that stars are orbited by planets as a rule, rather than
the exception." While other techniques are biased towards detecting
planets close to their stars (such that 17 to 30 percent of
Sol-type stars have been found to have
such inner-orbit planets), gravitional lensing has found reveals the
fraction of planets at farther orbits. In their survey of planets
within 0.5 to 10 AUs of their host star, the astronomers found that
17 +6/-9 percent of observed stars had Jupiter-class planets (of 0.3
to 10 Jupiter masses), 52 +22/-29 percent had Neptune-class planets
(of 10 to 30 Earth-masses), and that 62 +35/-37 percent had super-Earths
of 5 to 10 Earth-masses, which is consistent with the conclusion that
an average star in the Milky Way should have one or more planets within
an orbital distance of 0.5 to 10 AUs, and that there may be some 10
billion Earth-sized planets in the galaxy (ESO
press release;
Anil
Ananthaswamy, New Scientist, January 11, 2012;
Jason
Palmer, BBC News, January 11, 2012; and
Cassan
et al, 2012).

A planet detection effort using gravitational
microlensing suggests
that most stars in our galaxy have
planets in orbit around them, of
which many are super-Earths
(more).

On December 5, 2011, on the opening of its
inaugural
science conference at NASA's
Ames
Research Center, the
Kepler
Mission team announced 1,094 new
planetary candidates, bringing the running total of potential planet
discoveries to 2,326. Of those Kepler planetary candidates, 207 are
roughly Earth-size, 680 are super-Earth-size, 1,181 are
Neptune-size, 203 are Jupiter-size, and 55 are larger than Jupiter.
Based on Kepler observations conducted from May 2009 to September
2010, the planet findings show a dramatic increase in the numbers
of smaller-size planet candidates, where Earth-size and
super-Earth-size candidates have increased in number by more than
204 and 136 percent, respectively, since the last Kepler announcement
in February 2011. The new data indicate that planets from one to
four times the size of Earth may be abundant in our galaxy. Thus
far, Kepler has found 48 planetary candidates in their host star's
habitable zone (of which 10 are near Earth-size), but this number
is a decrease from the 54 reported in February 2011 only because
the Kepler team is now applying a stricter definition of what
constitutes a habitable zone around stars to account for the
warming effect of planetary atmospheres, which would move such a
zone away from the star, outwards in orbital distance resulting
in longer orbital periods (NASA
news
release; and Kepler Press Conference slides --
in pdf).

As Kepler 22 is slight smaller and cooler than
our Sun, Sol, its habitable zone is slightly
smaller and located closer to the star than the
habitable zone around our own Sun
(more).

In a pre-print submitted on
November 21, 2011, a team of astronomers revealed the finding
of a second potential
super-Earth "c" with
at least 3.4 Earth-masses in a potentially habitable-zone orbit
(~0.12 AUs) with a period of 28.1 days around Gliese 667 C, or
MLO 4 C,
(Bonfils et al, 2011;
and Delfosse et al, 2011, in prep).

HD 85512 b has some 3.6 Earth-masses
and appears to orbit near the estimated
inner edge of the
habitable zone
around
its host star, where liquid water, and
possibly life, may exist under favorable
conditions
(more).

A new super-Earth with around 10
Earth-masses (that may have a gaseous
atmospheric envelope of hydrogen and
helium like Uranus) has been detected
in a cold orbit around a dim, low-mass
star aroud 9,900 light-years away
(more).

On May 23, 2011, astronomers on the Kepler
Mission announced confirmation of another planet in the Kepler-10 system,
designated Kepler-10c. It's existence was "validated using a combination of
a computer simulation technique called 'Blender' and NASA's
Spitzer Space Telescope.
Kepler-10c appears to be a super-Earth class planet with 2.2 times Earth's
radius, and it orbits the star every 45 days (which is longer than
Kepler-10b's eight-day orbit and so must have a longer orbital distance).
Although also a super-Earth class planet, Kepler-10b has only 1.4 times
Earth's radius and has been determined to be one of the smallest rocky
planets detected thus far. Both Kepler-10b and 10c, however, are calculated
to be "blistering hot worlds" (Kepler
news
release;
Fressin et al, 2011; and
Francois Freesin's PowerPoint
presentation
slides).

A new super-Earth "c" has been detected
in the Kepler 10 system around 560
light-years away, which should be a
"blisteringly hot" world
(more).

On March 8, 2011, two astronomers analyzing the first
four months of data from NASA's
Kepler Mission
submitted a pre-print with an initial estimate that
the 1.4 (+/- 0.5) to 2.7 (+/- 0.9) percent of the Sun-like
stars (of FGK spectral types) in the Kepler sample of nearly
155,500 may host Earth- and super-Earth sized planets with
orbits within their host star's habitable zone
(Catanzarite
and Shao, 2011). The variance in the estimates
depended on the use of a conservative versus a more
conventional definition of habitable zone
(Kasting
et al, 1993; and
ExoPlanet
Task Force,
2008
report in pdf, pp. 102-103). Their calculations
suggested that Kepler will eventually find a total of 12
such "Earth-analog" planets after three to four years of
observation, and that four of these planets have already
been detected. The astronomers expect that this estimate
of Earth-analog planets can be refined as Kepler's data
set grows to 3.5 to six years of observations
(Catanzarite
and Shao, 2011; and
Victoria Jaggard, National Geographic News,
March 29, 2011).

A March 2011 study estimates that
1.4 to 2.7 percent of the Sun-like
stars (of spectral classes FGK) in
the 155,500 sample being observed
by NASA's Kepler
Mission may
host Earth- or Super-Earth sized
planets in habitable orbits
(more).

Using a smaller dataset over 6.5
rather than 11 years, a rival team
of astronomers has not been able
confirm the existence of planetary
candidates "g" and "f"
(more).

On September 29, 2010, a team of astronomers
announced the discovery of a super-Earth sized,
rocky planet orbiting within the habitable zone
of nearby, red dwarf star
Gliese 581
(also known as HO Librae but first catalogued as
BD-07 4003), based on 11 years of radial-velocity
measurements at the
Keck
Observatory and similar published data from the
Geneva
Observatory's
HARPS
project. Located towards Constellation
Libra,
the Gliese 581 system is now believed to have at
least six planetary candidates, of which the
"potentially habitable" planet has been designated
as Gl 581 "g."
This planetary candidate is
estimated to have between 3.1 and 4.3 Earth-masses
and between 1.3 and 1.5 times Earth's diameter, with
a greater surface gravity of around 1.1 to 1.7 g.

A new super-Earth with around 10
Earth-masses (that may have a gaseous
atmospheric envelope of hydrogen and
helium like Uranus) has been detected
in a cold orbit around a dim, low-mass
star aroud 9,900 light-years away
(more).

On May 23, 2011, astronomers on the Kepler
Mission announced confirmation of another planet in the Kepler-10 system,
designated Kepler-10c. It's existence was "validated using a combination of
a computer simulation technique called 'Blender' and NASA's
Spitzer Space Telescope.
Kepler-10c appears to be a super-Earth class planet with 2.2 times Earth's
radius, and it orbits the star every 45 days (which is longer than
Kepler-10b's eight-day orbit and so must have a longer orbital distance).
Although also a super-Earth class planet, Kepler-10b has only 1.4 times
Earth's radius and has been determined to be one of the smallest rocky
planets detected thus far. Both Kepler-10b and 10c, however, are calculated
to be "blistering hot worlds" (Kepler
news
release;
Fressin et al, 2011; and
Francois Freesin's PowerPoint
presentation
slides).

The Kepler Mission has detected
a rocky super-Earth in a torch orbit
around an old star around 560 years
away
(more).

On January 10, 2011, astronomers working with NASA's
Kepler space telescope announced
the discovery of a rocky super-Earth of only 1.4 Earth-diameters
across and around 4.6 Earth-masses, at the
217th Annual Meeting of the
American Astronomical Society. Designated "Kepler-10b," the
planetary candidate was already catalogued as Kepler Object of Interest
or (KOI) 72.01. It orbits an aged, spectral type G star (KIC 11904151)
of 0.895 Solar-mass and 1.06 Solar-diameter with around 1.00 Solar
luminosity, which is estimated to be at least 7.4 billion years old.
The Kepler-10 system lies around 560 light-years away in the northwestern
corner of Constellation
Cygnus.

Kepler 10b appears to
be a rocky planet that
is probably denser
than Earth
(more).

With a torch orbit around its host star that takes only about
20 hours (84 percent of an Earth day) to complete, Kepler 10b
has an average orbital distance of only 0.017 AU from its host
star and so has a tidally locked, synchronous orbit. Hence,
the planet has a perpetually daylight side with a
fequilibrium surface temperature of around 2,840 degrees
Fahrenheit (1,560 degrees Celsius), which is hotter than
molten lava and sufficient to melt iron. Kepler 10b was
detected using the
transit
method from more than eight months of data collected by the
spacecraft between May 2009 and early January 2010 and
confirmed by radial velocity measurements, and there evidence
for another planet (KOI 72.02) in an outer orbit with a period
around 45.3 days (Kepler
news
release;
images,
animations,
and
discovery
page; and
Batalha
et al, 2011).

Multiple planetary transits, including a confirmed
super-Earth (KOI 377.03 or Kepler-9d) with a
1.6-day period and 1.5 times Earth's diameter,
may have been detected for the first time by
the
Kepler
Mission
(more).

On August 25, 2010, NASA announced that the
Kepler
spacecraft had detected the first multiple
transits across a star other than the Sun, towards
Constellation
Lyra.
The Kepler observations indicate that two planets
of sub-Saturn size orbit the star designated
"Kepler-9" (or KOI-377), where the planet
"Kepler-9b" orbits closer to the star with an
period of about 19.2 days, while aouter planet
"Kepler-9c" has an orbit lasting about 38.9 days.
In addition, there are indications of an
innermost planetary candidate of super-Earth
size (Kepler Object of Interest / KOI 377.03 or
"Kepler-9d"), with only 1.64 +0.19/-0.14 times
Earth's diameter and a scorching orbit that lasts
only 1.6 days, which has been confirmed
(Torres
et al, 2011; NASA
press
release, with
supporting
charts and videos; CfA
news
release;
NASA
Science News; and
Holman
et al, 2010).

The Kepler Mission has detected the
possible transits of several hundred
potential super-Earth- and Earth-sized
planets around distant stars
(more).

On June 15, 2010, astronomers working on NASA's
Kepler
Mission released data on all but 400 of some
156,000 target stars. Some 706 stars from this
target list were found to have planetary candidates
after the first 43 days of observations,
but only the identity and some characteristics of
306 stars with at least one planetary candidate
were released, including those of five possible
multi-planet systems. The Kepler team is holding
back data on some 400 of the target stars that are
most likely to have Earth-sized -- with planetary
candidates of 1.4 Earth-diameters (radii) or
smaller within error margin -- and possibly
Earth-like planets for further study, until
re-scheduled release in February, 2011 (Kepler
news
release;
Dennis
Overbye, New York Times, June 15, 2010;
Nancy
Atkinson, Universe Today, June 15, 2010;
Dan
Vergano, USA Today, June 15, 2010;
Borucki
et al, 2010; and
Steffen
et al, 2010). Potential super-Earths -- all with
estimated diameters (or radii) between 1.5 and 2.2 that
of Earth's but with close-orbiting periods of less than
41 days -- that were found and released by the Kepler
Mission as part of its 306 stars with planetary candidates
are listed in the table below by designation number as a
"Kepler Object of Interest" (KOI).